SLAC-SD. Relevance of sea and land surface-atmosphere-climate interactions within the framework of statistical downscaling for Europe and the Mediterranean area.
Final Report Abstract
The research project provides an assessment of the impact of soil moisture (SM) and sea surface temperature (SST) on precipitation and temperature downscaling in the Euro- Mediterranean area. The objective was to develop a statistical downscaling procedure to model climate variables considering SM and SST as predictors in addition to commonly used atmospheric variables. Results showed an improvement of the skill of the statistical models when using SM information. This improvement was only moderate when averaging over the whole Euro-Mediterranean domain, but when looking at individual regions, the gain in performance can be substantial. The gain in statistical model skill when using SST as additional predictor was comparatively small, indicating a limited influence of lagged SST on climate in the Euro- Mediterranean region. One of the main findings was that SM centres of variation selected in the regression models as predictors can match with the location of the target precipitation region, but can also be located in other parts of the domain. It points to the importance of regional coupling mechanisms as well as to the relevance of moisture advection via the atmospheric circulation. The relationships of SM with precipitation were mostly positive, i.e. wetter soils lead to enhanced precipitation amounts in the subsequent months. The connection of SM with temperature was mostly negative, i.e. drier soils lead to above average air temperatures. Furthermore, the increase of statistical model performance when using SM as an additional predictor showed no dependence on the seasons and was rather scattered across the EU-MED domain. Importantly, statistical models for regions and seasons, which do not fit into the classical theoretical framework of SM-precipitation and SM-temperature coupling could substantially benefit from the inclusion of SM as additional predictor. In these cases teleconnections between preceding SM anomalies and subsequent precipitation/ temperature conditions occur, with modifications of the large-scale atmospheric circulation and humidity playing an important role. In this regard, the statistical modelling results diverge from the classical conceptual framework with local dependency of evaporation on SM, which is commonly used to understand SM-precipitation and SM-temperature relationships in current GCMs. The statistical projections under climate change conditions were also impacted by the use of SM as an additional predictor. While there were mostly only small changes in spring, summer, and autumn, particularly winter climate was affected by the inclusion of SM. For instance, winter increases in precipitation projected for most of the central, eastern and northern parts of Europe were substantially lower by comparison with the results obtained with a downscaling setting based only on atmospheric predictors. The statistically established SM-precipitation teleconnections considerably modify EU winter precipitation through SM signals from the southern parts of the domain. Within the findings of the current research project the following issue is explicitly highlighted: there are potentially shortcomings in the representation of SM forcing on climate in the GCMs. While in GCMs mostly the local land-atmosphere-climate interactions are focused on, the statistical results of this study suggest that also large-scale SM-atmosphere-climate teleconnections play an important role. One could argue that in the dynamical ESMs the influence of SM on climate should be completely included by modifications of the atmospheric circulation. Thus, atmospheric predictors alone would suffice to statistically downscale local/ regional climate. However, if the relevant SM anomalies were already properly incorporated in the atmospheric link in ESMs, the differences in the predictand between the correspondent statistical model settings should be insignificant. However, we showed that the explicit inclusion of SM in the downscaling equations impacted strongly on the downscaling results.
Publications
- Landoberflächen-Atmosphäre-Wechselwirkungen in Europa und dem Mittelmeerraum. 34. Jahrestagung des AK Klima der Deutschen Gesellschaft für Geographie, Hattingen an der Ruhr, 30.10.-1.11.2015
Romberg, K., Hertig, E., Jacobeit, J.
- (2016): Non-stationarities in land-atmosphere-climate interactions in Europe and the Mediterranean region. Geophysical Research Abstracts, Vol. 18, EGU2016-12346, Vienna, Austria, 17.-22.4.2016
Romberg, K., Hertig, E., Jacobeit, J.
- (2016): Regional downscaling of Mediterranean droughts under past and future climatic conditions. Global and Planetary Change
Hertig, E., Tramblay, Y.
(See online at https://doi.org/10.1016/j.gloPlacha.2016.10.015) - (2017): Bodenfeuchte als Prädiktor im Niederschlagsdownscaling für den europäischen und mediterranen Raum. 36. Jahrestagung des AK Klima der Deutschen Gesellschaft für Geographie
Hertig, E., Tramblay, Y., Romberg, K., Kaspar-Ott, I.
- (2018): Bedeutung der Bodenfeuchte im Niederschlagsdownscaling für den euro-mediterranen Raum. 37. Jahrestagung des AK Klima der Deutschen Gesellschaft für Geographie
Hertig, E., Tramblay, Y., Romberg, K., Kaspar-Ott, I, Merkenschlager, Ch.
- (2018): Modelling extreme dry spells in the Mediterranean region in connection with atmospheric circulation. Atmospheric Research, 202, 40-48
Tramblay, Y., Hertig, E.
(See online at https://doi.org/10.1016/j.atmosres.2017.11.015) - (2018): The impact of soil moisture on precipitation downscaling in the Euro-Mediterranean area. Climate Dynamics, 52(5), 2869-2884
Hertig, E., Tramblay, Y., Romberg, K., Kaspar-Ott, I., Merkenschlager, Ch.
(See online at https://doi.org/10.1007/s00382-018-4304-2) - Statistical downscaling of temperature over the Euro-Mediterranean region: the role of sea surface temperature and soil moisture as additional predictors. Geophysical Research Abstracts, Vol. 19, EGU2019-10012-1, 2019
Pomee, M.S., Hertig, E.
